The activists said Thursday the documents could show whether the federal government did enough to clean up the site before turning part of it into a wildlife refuge and opening it to the public.

Rocky Flats made plutonium triggers for nuclear bombs until 1989, when it was shut down after a series of fires and accidental releases. After a grand jury investigation, the plant operator pleaded guilty to environmental violations and was fined $18.5 million.

The grand jury records are still sealed.

The plant site was cleaned up but remains off-limits. A buffer zone around the plant became a wildlife refuge and was opened to the public last fall.